Planarization of copper damascene using reverse current electroplating and chemical mechanical polishing

Abstract

Methods are disclosed to improve the planarization of copper damascene by the steps of patterning on the copper damascene a photoresist using a reverse tone photo mask or a reverse tone photo mask of the metal lines, removing excess copper by reverse current plating or by dry or wet chemical etching, stripping the photo resist, and a subsequent chemical mechanical planarization of the copper damascene. Lastly a cap layer is applied to the planarized surface. In a variant of the disclosed method a more relaxed reverse tone photo mask of the metal lines is used, which may be more desirable for practical use. These steps provide benefits such as improved uniformity of the wafer surface, reduce the dishing of metal lines (trenches) and pads, and reduce oxide erosion.

What is claimed is:  
     
       1. A method of forming and planarizing copper layer, comprising the steps of: 
       providing a substrate;  
       forming dual damascene trenches in said substrate;  
       depositing a barrier metal layer on said substrate and in said dual damascene trenches;  
       depositing a seed layer on top of said barrier metal layer;  
       electroplating a copper layer on top of said seed layer by means of forward current electroplating;  
       forming a reverse tone photoresist mask;  
       etching away that part of said copper layer and said barrier metal layer not covered by said reverse tone photoresist mask by means of reverse current electroplating;  
       stripping of said photoresist;  
       planarizing by chemical mechanical polishing (CMP) said now exposed copper layer and barrier metal layer; and  
       sealing said copper layer with a cap layer.  
     
     
       2. The method of  claim 1 , wherein said dual damascene trenches are patterned into a silicon oxide layer of a silicon semiconductor wafer. 
     
     
       3. The method of  claim 1 , wherein said substrate is a silicon oxide layer of a silicon semiconductor wafer. 
     
     
       4. The method of  claim 1 , wherein said reverse tone photoresist mask is a photoresist mask covering that part of said copper layer which is in said trenches. 
     
     
       5. The method of  claim 1 , wherein said reverse tone photoresist mask also covers spaces between said damascene trenches having a separation of less than a critical distance. 
     
     
       6. The method of  claim 5 , wherein said critical distance ranges from 0.05 μm to 0.2 μm.